Surge testing will take place from Monday after cases of the Brazil COVID-19 "variant of concern" were found in England and Scotland.
The variant is the latest to be detected in the UK as the government hopes to reduce transmission through lockdown measures and the vaccine roll-out.
Sky News takes a look at where the new variant was found, whether it is more transmissible than other strains, and if vaccines will work to stop infection.
What is the Brazil 'variant of concern'?
The variant, called P1, is a branch of the B.1.1.28 lineage that was first detected in Japanese travellers who had visited Brazil, the Centers for Disease Control and Prevention (CDC) has said.
It has three mutations in its spike protein receptor binding domain.
It was designated "of concern" as it shares some important mutations with the variant first identified in South Africa.
P1 is tought to have originated in the city of Manaus in Brazil and has since been found in Japan and several other European countries.
Is this variant more dangerous or transmissible than others?
The spike protein mutations mean P1 is likely to be more transmissible than its parent strain, researchers told Medical News.
It is unclear whether it is more transmissible than the other variants that have been found in the UK.
It is also not known whether its mutations mean it causes a more severe infection.
Where in the UK has it been found?
Three cases of the new variant have been found in South Gloucestershire, Public Health England said on Sunday.
Two of the cases come from a household in the area.
One person in the household had returned from Brazil in mid-February before the new hotel quarantine measures were introduced.
The third case is unlinked and the whereabouts of the individual unknown, as the person did not complete their test registration card, PHE said.
Scotland's three variant cases have been identified in the Grampian region in the north of the country after three people flew from Brazil to Aberdeen via Paris and London earlier this month.
All the other passengers who were on their final flight from London to Aberdeen have been contacted, the Scottish government said.
Where will surge testing take place?
Surge testing will now take place in South Gloucestershire.
Residents who live in five postcode areas, who are aged over 16 and do not have symptoms of COVID-19, are invited to come forward for testing.
People who travel into the areas - BS32 0, BS32 8, BS32 9, BS34 5 and BS34 6 - for work or to visit someone they are in a support bubble with are also able to have a test.
It not yet clear if surge testing will take place in response to the cases found in Scotland.
Do the vaccines work against it?
The CDC has said the spike protein mutations affect the virus' "antigenic profile".
They added this "may affect the ability of antibodies generated through a previous natural infection or through vaccination to recognize and neutralize the virus".
Health officials say it is "possible" vaccines may be less effective against it, but more work is needed to establish whether that is the case.